One typical employment of such containers is as a mold in a tire retreading operation, where a set of several tires are held on top of one another in a cylindrical tub under axial pressure while being cured. Such tires are manually loaded and unloaded thereby requiring a removable insert pressure member at the top of the tire stack. Conventionally in the art some mechanisms provide a hydraulic lift with a long stroke. This has a serious disadvantage of the height of the unit required and the dependence upon expensive hydraulic servo systems.
Other mechanisms provide for manually adjustable clamping means comprising a single screw or bayonet assembly axially mounted in the cylinder. This has the significant disadvantage that there is a tendency of the insert to tilt especially under curing pressure. This could lead to release of steam and danger to workers as well as improper cure.
In general, the insert must cause a sealing pressure to be exerted upon a stack of tires which in retreading operations may have mixed dimensions and not be uniform in height. Thus, an axial adjustment of the insert position and force within the cylinder is required. Yet the mold must be easy to operate and not require significant labor in loading and unloading.